This invention is directed to a helical seal for sealing between cylindrical sliding members. The helical seal is stressed so that part of the seal engages against the stationary member and part engages against the moving member. The seal is stressed so that it unwinds when wear takes place to supply further material subject to wear and maintains sealing force.
The provision of a long life seal between reciprocating parts has long been a design challenge. The challenge is particularly severe where the seal is not provided with a lubricant from an external source, or is operated in a vacuum or other difficult environment. Previous types of seal configuration required compression of a resilient seal material followed by the return of the seal material to its previous configuration. "O" ring seals of that type are made of rubber-like synthetic polymer composition materials, made of polytetrafluoroethylene or the like. They have a limited amount of material which can wear away before the seal becomes ineffective. Some "C" section seals wear in the same manner, but sometimes have garter springs therein to provide additional force to increase sealing forces. Other seals have a gap between facing ends. The internal combustion engine piston ring seal is of this nature. Furthermore, there are segmented seals having wedge-shaped segments which expand as the material wears away.
Thus, there is a need for an improved seal for application between sliding parts, particularly for the sealing around pistons and piston rods, and particularly in environments where lubrication is difficult, or in environments where separate lubrication can not be applied because it would contaminate the fluid being controlled by the seal.